perf arch x86: Add missing stdlib.h to get free() prototype

It was getting indirectly, out of luck, add it.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/x86/util/event.c

@@ -2,6 +2,7 @@
 #include <linux/types.h>
 #include <linux/string.h>
 #include <linux/zalloc.h>
+#include <stdlib.h>
 
 #include "../../../util/event.h"
 #include "../../../util/synthetic-events.h"

tools/perf/arch/x86/util/tsc.c

@@ -2,6 +2,7 @@
 #include <linux/types.h>
 #include <math.h>
 #include <string.h>
+#include <stdlib.h>
 
 #include "../../../util/debug.h"
 #include "../../../util/tsc.h"